This invention relates to tissue welding, more particularly, to a method by which tissue may be welded reliably under controlled conditions. Lasers of various types have long been used in various medical applications. In a wide variety of surgical techniques, laser light is used to cut tissue, and to coagulate simultaneously along the cut. Some progress has been made previously, in the use of laser energy for joining tissue, commonly termed tissue welding. The ultimate goal is to facilitate the joining of tissues with a minimum of scar tissue formation, and high tensile strength at the joined edges. Progress in the field of laser tissue welding has been slow due, in part, to the large number of laser parameters that need to be considered in the welding process. These parameters include wavelength, radiant exposure, irradiance, pulse duration, pulse repetition rate, irradiation time, spot size, dye selection, and adhesive selection. Past tissue welding studies have used a wide range of values for these welding parameters, making the interpretation of results and comparison between studies difficult.
The majority of previous tissue welding studies have used a laser operated in either continuous wave (CW) mode or quasi-CW mode with constant surface temperature control. During CW and temperature-controlled welding, heat diffuses from the weld site into surrounding healthy tissue, typically resulting in a large zone of thermal damage. A zone of thermal damage greater than .about.200 .mu.m extending laterally from the weld site may inhibit wound healing and result in excessive scarring. For some applications, such as skin welding, too much scar tissue may be clinically unacceptable even if strong welds can be achieved.